I'm making a question on the explosion of hydrogen/oxygen. All the things you need to know are the following. The formation of H-radicals in the H2-O2 mixture are responsible for ignition of the explosion. This means the H-radicals need to be formed faster than they are destructed to let the mixture explode. One of the 'termination' reaction in which H-radicals are removed is through collisions with the vessel wall.

H + wall --> removal with rate constant k_1

The question now is: "Textbooks state that the rate constant k1 can be written as:
k_1 = k_d / P with P the total pressure and k_d another rate constant. Assuming that the vessel is spherical with radius R, and d is the diameter of a hydrogen atom, and m its mass. Derive now the following equation: